Scintillators are materials that absorb high energy radiation, such as α-, β, γ-rays, X-rays, neutrons or other high energetic particles, and convert that energy into bursts of visible photons. In detectors for the above mentioned radiation, these photons are then converted into electrical pulses by photo-detectors.
Alternatively the radiation is converted directly in a semiconductor which is sandwiched between two electrodes. In a detector the initially created electron-hole-pairs are separated by an externally applied electric field and the resulting electrical current sensed by an amplifier. Various materials for direct conversion detectors for X-ray radiation are described, for example, in “Amorphous and Polycrystalline Photoconductors for Direct Conversion Flat Panel X-Ray Image Sensors” by S. Kasap et al. (Sensors 2011, 11, 5112-5157 (2011)). U.S. Pat. No. 5,132,541 addresses applications in flat X-ray detectors.
Already for quite some time, inorganic-organic halide Perovskites have been investigated for several applications. One of them is scintillators, see, for example, “Quantum confinement for large light output from pure semiconducting scintillators” by K. Shibuya et al. (Applied Physics Letters, vol. 84, no. 22, p. 4370-4372). Such systems have also been investigated for EL-light-emission and photovoltaics (PV) with very high efficiencies, see, for example, “Organic-inorganic heterostructure electroluminescent device using a layered perovskite semiconductor (C6H5C2H4NH3)2PbI4” by M. Era et al. (Appl. Phys. Lett. 65 (6), p. 676-678, August 1994) and “The light and shade of perovskite solar cells” by M. Grätzel (Nature Materials, Vol. 13, 2014, p. 838-842).
Perovskite materials are also known to act as a light emitter, see, for example, “Bright light-emitting diodes based on organometal halide perovskite” by Z.-K. Tan et al. (Nature Nanotechnology, vol. 9, p. 687-692, 2014).
EP 1 258 736 A1 relates to a radiation detection device for detecting ionizing beam discharges such as gamma rays, x-rays, electron beams, charged particle beams and neutral particle beams. Specifically, it relates to a radiation detection device which can measure radiations which exist for a very short time (of the order of subnanoseconds or less) from the appearance of photoemission to extinction.
It is an object of EP 1 258 736 A1 to provide a radiation detection device using a perovskite organic-inorganic hybrid compound as a scintillator, the formula of this compound being (R1—NR113)2MX4 or (R2═NR122)2MX4, or alternatively, (NR133-R3—NR133)MX4 or (NR142═R4═NR142)MX4 (in the formula, R1 is a monovalent hydrocarbon group which may contain a heterocyclic ring and may be substituted by halogen atoms, R2 is a divalent hydrocarbon group which may contain a heterocyclic ring and may be substituted by halogen atoms, and may be cyclic, R3 is a divalent hydrocarbon group which may contain a heterocyclic ring and may be substituted by halogen atoms, R4 is a tetravalent hydrocarbon group which may contain a heterocyclic ring and may be substituted by halogen atoms, R11-R14 may be identical or different, and may be hydrogen atoms or alkyl groups having two or more atoms, M is a Group IVa metal, Eu, Cd, Cu, Fe, Mn or Pd, and X is a halogen atom). This radiation detection device can quantify the radiation amount of the detected radiation.
An interesting application of the inorganic-organic halide Perovskites are X-ray detectors. In order to fabricate an X-ray detector based on the inorganic-organic halide Perovskites, a comparatively thick layer of the Perovskite appears to be needed. Growing single crystals is known, however it is not yet known how to efficiently grow a thick (poly) crystalline layer on a substrate.
For spatial X-ray detection a structured set of separate detectors is required. This can be fabricated by structuring the bottom electrode, depositing a Perovskite layer and depositing a cathode on top. Apart from the bottom electrode structuring, the process is quite similar to the Perovskite-PV process. However, for PV only Perovskite layers of around 300 nm have to be deposited. This can be done by spin-coating or physical or chemical vapor deposition. For layers above 10 μm thick this is not possible and/or affordable.